Pneumatic surgical staplers have become one of the preferred alternative methods to manually driven surgical staplers. An advantage of a pneumatic surgical stapler is that the force needed to fire the stapler is controlled by the driving mechanism, and not the strength of the user. In a pneumatic stapler, a compressed gas line or compressed gas cartridge releases gas pressure in order to activate the driving mechanism in the surgical stapler. In a reliable pneumatically driven surgical stapling mechanism, the force required to fire the staple is repeatably derived within a very refined tolerance. Thus, in a pneumatic surgical stapler there is the assurance that a repeatable force-to-fire is derived.
One of the ways in which pneumatic surgical staplers operate is through means of an inflatable elastomeric bladder. Bladders convert pneumatic pressure into motion within the limitably accessible head of the surgical stapler. A bladder operates by expanding from pressurized fluid inserted into an opening in the bladder. The fluid is generally carbon dioxide gas and is introduced through a tube inserted in the opening in one end of a sock-like bladder. The tube and bladder have previously been connected to each other by means of a mechanical clamp. The bladder forms a type of gasket between the clamping parts and the tube.
Introduction of carbon dioxide causes inflation of the bladder and can be converted to movement of various mechanisms in, for example, the head of a linear surgical stapler.
For the stapler to be a limited access device, the combination of bladder, tubing and stapling head must meet severe dimensional constraints. The bladder, tubing and driving mechanism must all fit within a linear stapling head which fits within the body. In general, the typical bladders used have a bottle-necked configuration which permits the smallest union between tube, bladder and clamping mechanism.
Bladders are made in a variety of ways including a latex dipping process using a mandrel. The mandrel has the configuration of the interior of the bladder and is dipped into liquid latex. The later is allowed to cure or solidify around the mandrel, resulting in a bladder.
A manufacturing problem is encountered in the necked region of the bladder. At this neckdown, it is extremely difficult to remove the bladder from the mandrel. The generally elastomeric latex bladder must be stretched over the shoulders of a mandrel and pulled from the bottom of the necking configuration. This procedure is time consuming and labor intensive and adds to the cost of making the part.
In addition, this assembly must be made in a tight fit, particularly since addition of any lubricant for tube insertion within the bladder combination may jeopardize later function of the stapling assembly.
Also, after firing, rapid deflation of the bladder in the stapling head can result in bladder material closing the orifice of a supply tube. Fluid becomes trapped when this orifice is blocked before complete deflation/inflation. Total deflation is limited due to the sealing off of the bladder material.
Additionally, dimensional interference between the clamping mechanism which holds the bladder on the tube and the tubing mechanism which inflates the bladder can result in crimping of the tubing mechanism. This results in flow restriction and decreased speed of closure of the clamping mechanism.
It is necessary to correct these problems for pneumatic stapling to be a desirable alternative procedure.